(1) Field of the Invention
The present invention relates to digital telephone offices and more particularly to a method for minimizing the number of Pulse Code Modulation (PCM) processing circuits associated with line circuits for such telephone offices. The line circuit is separated into an analog line circuit portion and PCM processing circuitry. An analog network is connected to the analog line circuits to provide concentration to a minimal number of PCM processing circuits.
(2) Description of the Prior Art
Line circuits for digital telephone end offices are of a hybrid nature in that they use analog circuitry for interfacing to the various subscriber stations and they are Pulse Code Modulation (PCM) circuitry for interfacing to the digital network of the digital telephone office. These line circuits are complex and expensive, and numerous varieties of them are required to operate with the numerous types of subscriber equipment, such as party lines, coin telephones, etc. Every line circuit requires loop status circuitry, but PCM processing circuitry, coin detection circuitry, party line circuitry, line testing circuitry and line simulation circuitry need not be dedicated to the corresponding line circuits. Therefore, by separating the analog line circuit into common analog line circuitry, PCM processing circuitry and specialized analog line circuitry, the highly complex and expensive PCM processing circuitry can be minimized since it will only be used when a subscriber is connected to the digital network. Similarly, the specialized analog line circuitry can be minimized since it will only be used when the associated specialized analog functions are performed. Also, the line circuit which must be provided for each line now comprises only the minimal common line circuitry for the supervisory function and can be used for any type of subscriber.
Accordingly, it is the object of the present invention to provide a novel arrangement for minimizing the required number of PCM line processing circuits in a digital telephone office. Additional features of this invention are a minimal component, common line circuit and minimization of specialized analog line circuitry.